Because Kessler unified the WBC/WBA regular titles he became what the WBA call 'unified champ'(there is also the status of Super champion for holding 3/4 belts) , once a fighter has achieved this in a division the WBA have a vacant title fight for the regular title .

The regular title holder cannot unify if there is already a Super champion/unified champion etc in the division .

The first example of 2 WBA champs was I believe in 2001 as William Joppy beat Howard Eastman for the regular WBA middleweight title with Bernard Hopkins as the Super Champion having beaten Tito Trinidad to become WBA champion having already held the WBC and IBF middleweight titles .

Yes it is ridiculous and an obvious ploy to earn sanctioning fees and frankly I detest it . There is one small positive and that's that the Super champion has 18 months to make a mandatory defence against the regular champion . That means a unified champion is much less likely to lose his belts through not defending mandatories and allows time for what are often more meaningful fights .